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2020-09-08, 20:02   #375
bur

Aug 2020

97 Posts

Quote:
 Originally Posted by VBCurtis Nope. But the opposite isn't true, either.
But then I would say low weight doesn't really matter. Either I test 100000 candidates for a given k and find 10 primes or I test 10000 and find one. Then move to the next low weight k and in the end I end up with the same number of LLRs and primes. Just spread over more than one k. Is it like that?

 2020-09-08, 23:30 #376 VBCurtis     "Curtis" Feb 2005 Riverside, CA 3·1,579 Posts We have no evidence otherwise, though some folks around here do think otherwise. I test a couple low-weight k's as well as some of the highest; I like finding anomalies, but I don't think my choices are more prime-worthy per unit of search effort.
 2020-09-09, 07:21 #377 bur   Aug 2020 11000012 Posts I looked into the matter why only primes show up as n for low n values. Here are some restrictions I found: If $n \equiv 0 \textrm{ mod } 2$ the Riesel number will be divisible by 3 (n = 2, 4, 6, 8, 10, ...) If $n \equiv 1 \textrm{ mod } 10$ the Riesel number will be divisible by 11 (n = 11, 21, 31, 41, 51, ...) If $n \equiv 1 \textrm{ mod } 8$ the Riesel number will be divisible by 17 (n = 9, 17, 25, 33, 41, 49, ...) If $n \equiv 15 \textrm{ mod } 20$ the Riesel number will be divisible by 41 (n = 15, 35, 55, 75, ...) If $n \equiv 19 \textrm{ mod } 70$ the Riesel number will be divisible by 71 (n = 19, 89, 159, 229, ...) There might be more. I am not sure though if this will rather hit composites than primes. The 2nd condition removes 11, 31, 41, 71, so it doesn't really seem like it. Last fiddled with by bur on 2020-09-09 at 07:35
 2020-09-09, 09:54 #378 bur   Aug 2020 97 Posts Haha, I just realized this is probably trivial and occurs for every divisor... yes, I'm not that good at math. :)
 2020-09-09, 20:46 #379 bur   Aug 2020 11000012 Posts Here are the n values for Riesel primes with k = 1281979 and n <= 100000 3 7 43 79 107 157 269 307 373 397 1005 1013 1765 1987 2269 6623 7083 7365 10199 16219 26143 32557 38165 47167 47863 70373 94723 95167
 2020-09-19, 13:26 #380 Happy5214     "Alexander" Nov 2008 The Alamo City 2×7×41 Posts The (near-)Woodall k's listed in https://www.mersenneforum.org/showpo...&postcount=363, again except for k=1993191, have been completed to n=375k. The only prime found was 667071*2^373497-1. Edit: Another prime, 667071*2^358286-1, was already reported (by me) to the Prime-Wiki in August, so I accidentally left it off here. Last fiddled with by Happy5214 on 2020-09-19 at 13:38 Reason: Forgot a prime
2020-10-01, 11:16   #381
Happy5214

"Alexander"
Nov 2008
The Alamo City

2·7·41 Posts

I've completed the remaining RPS 9th and 10th Drive k's with missing ranges from n=300k to 325k. 18 primes were found, which are attached. It'll probably be until the end of 2021 before they're finished to n=400k, the ultimate goal.
Attached Files
 RPS_300-325K.txt (255 Bytes, 117 views)

 2020-11-04, 02:26 #382 Dylan14     "Dylan" Mar 2017 23D16 Posts update 11/3 k = 50171 is at 3.883 M, is on hold for the moment while I do a Carol-Kynea reservation. Please keep it reserved to me.
 2020-11-07, 08:46 #383 Nescro   Jun 2020 1112 Posts 8847 Reserving 8847
 2020-11-18, 08:47 #384 Happy5214     "Alexander" Nov 2008 The Alamo City 2×7×41 Posts The (near-)Woodall k's listed in https://www.mersenneforum.org/showpo...&postcount=363, this time and in the future including k=1993191, have been completed to n=400k. The primes for k=1993191 have already been posted to Prime-Wiki and will not be listed here for the sake of brevity. (There are 26 total below n=400k.) The following primes were found for the other k's:667071*2^380058-1 1183953*2^384787-1 665127*2^385516-1 1268979*2^387863-1
2020-11-27, 01:33   #385
diep

Sep 2006
The Netherlands

26×11 Posts

Quote:
 Originally Posted by bur But then I would say low weight doesn't really matter. Either I test 100000 candidates for a given k and find 10 primes or I test 10000 and find one. Then move to the next low weight k and in the end I end up with the same number of LLRs and primes. Just spread over more than one k. Is it like that?
Given: k * 2^n - 1

The risk you run with low-weights is that you do not find a prime at all,
because when the number of bits of the exponent n increases, the testing time goes exponentially up and there is going to be a limit that your hardware can quickly enough proces.

See a low weight as a big gamble.

Yet i'm also gambling upon one.

So currently actively i'm searching k=32767 (low weight) and k=89 (medium to heavy weight).

k=69 has been temporarily stopped, for a simple reason. My hardware has problems crunching above n=7Mbits - the L2 cache simply isn't large enough.

Nash-weight of course is a quick estimate.

Note that i'm also sieving k=32767 deeper and deeper. I'm now at a point that for quite a while sieving deeper is more useful than testing. With k=32767 that's roughly around n = 5Mbits for my hardware.

Note i started sieving until 30Mbits. So right now i'm sieving [5M ; 30M]

Probably that's becasue of wishful thinking from my side i ever will manage to get that far.

As i'm still removing quite a bit of exponents at larger sieve depths i would expect the odds for a prime is dramatically lower than one would expect for a different k with the same nash-weight where this sieving heuristic doesn't apply.

So if i'm so lucky i find 1 prime with k=32767 worth mentionning, yet odds is huge there isn't one. If the next k=32767 prime is located at 25Mbits then i'm not sure i'm gonna find it before having entirely white hair (and right now it's not yet grey) :)

For some small odds of finding 1 prime would you want to do all this effort and wait that many years?

On the other hand k=89 i need to do 20k tests between 4m and 5m - yet that'll take only a year or so. And 5m to 6m i do not know yet. Will depend upon whether i make enough cash to upgrade the hardware here :) Read - whether my 3d printer finally releases after that many years...

Yet odds are quite optimistic there is 1 or more primes between [4m and 8m].

The low weight is a total gamble and basically i probably am soon going to take the decision to just sieve [5m ; 30m] for a year to come. No nothing testing above 5M for now...

A single core from a magny cours processor here of 2.2Ghz removes on average 1 exponent each 3+ hours.

We can calculate the break even point when to start testing [5m;6m]
Well that's a 2:20 AM estimate here just typed in live.

BSGS algorithm works uses a square root trick you can find on wiki.
So we can see [5m ; 30m] versus [6m ; 30m] for sieving.

sqrt(24 mln) / sqrt (25mln) = 0.9797

So that's roughly 2%, So the sieving is 2% slower roughly if i keep testing the larger domain [5m;30m]

Now testing time at [4m;5m] is already 15000 seconds at 2 cores of a Xeon L5420 at 2.5Ghz. That's 8.3 hours for 1 core.

We assume an even distribution the sieving gets where it removes an exponent between [5m and 30m]

So when under this circumstance is there a break even point of testing expressed in removal rate?

A first attempt to calculate break-even point.... (yeah at 2:30 AM by now)...

Let's assume now that the average of [5m ; 6m] is 5.8M.

LLR time for 5.8M might be roughly 8.3 hours * (5.8M / 4.0M) ^ 2 = 17.5 hours

17.5 hours == removal_rate * 0.02 * (25M / 1M)

==> removalrate = (17.5 hours * 50 / 25) = 17.5 * 2 = 35 hours

So i might be sieving for years to come before i can start testing the low weight k=32767 :)

removal_rate

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